The present invention relates to a method and apparatus for the transfer of relatively flat objects from a first work station and, more particularly, to the means by which the object to be transferred is propelled from the work station. The present invention is especially adapted for use within equipment for the manufacture of shells used to close the ends of metal cans.
One common way of packaging liquids, foods and other products, particularly beer, soft drinks, juices and the like, is within cans typically formed from aluminum or steel. In such cans, the can body is either manufactured to include both the can side walls and an attached bottom end, or the bottom end is formed separately and subsequently joined to the side walls. The upper end, which includes the means by which the can is later opened, is manufactured separately and attached to the can body after the can has been filled. The can ends, often referred to within the art as shells, are generally manufactured within ram presses. While various particular methods of shell formation are known and available, it is often necessary as a part of these methods to transfer the shells from a first to a succeeding work station. In any case, it is also necessary to transfer the shells from a work station out of the press. In view of the large quantities of cans and shells that are manufactured, it is desirable to be able to form quantities of the shells very rapidly. This necessitates a transfer system that is both quick and reliable.
Various types of transfer systems for shells are known. In one approach, the shell is partially formed within the first tooling station and then positioned for transfer. A device is actuated to strike the shell with an edgewise blow that propels the shell outwardly from the tooling. The shell moves lateral-y along a transfer path either out of the press for further processing, or to a second station within the press for additional operations.
An example of this type of transfer system may be seen in U.S. Pat. No. 4,561,280. There, a driver extends an actuator to provide the blow for moving the shell along the transfer path. Ideally, the shell moves in free flight without contacting the restraining structure defining the path until the shell is captured at the second station. This system has been found to work well. However, it is not unusual for shell forming presses to be operated at speeds in excess of 24,000 strokes per hour. Such rapid and repetitive action takes a significant toll on mechanical devices. Thus, while the driver described above is specifically designed for speed and reliability, failures of the mechanical drivers would not be totally unexpected. Moreover, it would not be unusual for the driver mechanism to develop an unwanted sticking effect, whereby extension or retraction of the shell driving actuator could be slightly delayed.
Particularly where a shell is being transferred into a second work station within the same press, speed and consistency in transfer times is of great importance. Thus, it is not only necessary that the shell drivers continue to function, but that they continue to operate with optimum performance. Otherwise, shells could be delayed in being discharged from the press work station. While it might be possible to provide detectors for determining the occasional late arrival of shells at a second station, there is no practical way of delaying operations in the stations since such operations are under the control of the press drive. With the press running at speeds of several hundred strokes per minute, the timing of individual strokes cannot be altered. Thus, a late arriving shell could be subjected to forming or other work steps prior to proper positioning within the tooling. At best, this result in a deformed workpiece, but could also cause disruption of the manufacturing process requiring restarting of the press, removal of lodged workpieces, or even repair to damage to the press tooling itself
It can be seen, therefore, that any improvement in the transfer mechanism for moving shells from a press tooling and directing them into a transfer path is advantageous. Such improvements that increase either the speed or reliability of the transfer process will be reflected in a smaller number of defective shells and greater reliability of the press operation as a whole.